The present invention relates to the production of recombinant proteins using yeast host cells as the expression system. More particularly, it relates to compositions and methods for expression of heterologous proteins and their secretion as the biologically active mature proteins.
Yeast host expression systems have been used to express and secrete proteins foreign to yeast. Numerous approaches have been developed in terms of the degree of expression and the yield of biologically active mature proteins.
Such approaches have involved modifications to the various molecular components that are involved in expression and secretion of proteins in yeast. These components include the translation and termination regulatory regions for gene expression; signal peptide and secretion leader peptide sequences, which direct the precursor form of the heterologous protein through the yeast secretory pathway; and processing sites, which cleave leader peptide sequences from the polypeptide sequence of the protein of interest.
Expression of the protein of interest can be enhanced with use of yeast-recognized regulatory regions. Increased yield of the heterologous protein of interest is commonly achieved with the use of yeast-derived signal and secretion leader peptide sequences. The use of native signal-leader peptide sequences is believed to improve direction of the protein of interest through the secretory pathway of the yeast host.
Previous work has demonstrated that full-length yeast xcex1-factor signal-leader sequences can be used to drive expression and processing of heterologous proteins in yeast host cells. Substantial improvements in efficiency of expression can be accomplished with the use of truncated xcex1-factor leader sequences, particularly for heterologous proteins that are poorly expressed by the full-length sequence or whose expression is nonresponsive to the full-length sequence.
Although the various approaches available in the art have been shown to work with some proteins, problems persist with post-translational processing. Often the amount of protein secreted is unacceptably low or incorrect processing leads to inactive forms of the protein. This is particularly true for proteins that are initially expressed as a precursor polypeptide sequence and whose assumption of a native conformation is facilitated by the presence of a native propeptide sequence in the precursor polypeptide.
Methods for expression of heterologous proteins and their secretion in a biologically active mature form using a yeast host cell as the expression system are needed.
Compositions and methods for expression of heterologous proteins, more particularly heterologous mammalian proteins, and their secretion in a biologically active mature form using a yeast host cell as the expression system are provided. Compositions of the invention are nucleotide sequences encoding a signal sequence for a yeast secreted protein, a native propeptide leader sequence for a mature protein of interest, and a peptide sequence for the mature protein of interest. Each of these elements is associated with a processing site recognized in vivo by a yeast proteolytic enzyme. Any or all of these processing sites may be a preferred processing site that has been modified or synthetically derived for more efficient cleavage in vivo. In turn, all of these elements are operably linked to a yeast promoter and optionally other regulatory sequences.
The nucleotide coding sequences of these compositions may additionally comprise a leader peptide sequence for a yeast secreted protein. When present, this element, which is also associated with a processing site recognized in vivo by a yeast proteolytic enzyme, is positioned 3xe2x80x2 to the yeast signal sequence and 5xe2x80x2 to the sequence for the mature protein of interest. Thus cleavage by a yeast proteolytic enzyme removes the yeast leader sequence from the hybrid precursor molecule comprising the sequence for the mature protein of interest.
These compositions are useful in methods for expression of heterologous mammalian proteins and their secretion in the biologically active mature form. Particularly, vectors comprising these nucleotide coding sequences can be used to transform a yeast host cell, which can then be cultured and screened for secretion of the biologically active mature protein of interest.
The method of the present invention is particularly useful in production of mammalian proteins whose assumption of a native confirmation is facilitated by the presence of a native propeptide sequence in the precursor polypeptide.